NIST hawks microwave-based quantum computers

PORTLAND, Ore.—The National Institute of Standards and Technology (NIST) recently demonstrated a microwave technique for performing quantum entanglement, opening the door for inexpensive quantum computers to perform what so far only been possible with expensive lasers.

According to NIST, quantum entanglement will be the primary method for transporting information and performing error correction in future quantum computers.

Microwave technology—the technology used to carry the signals sent and received by cell phones—is a mature semiconductor technology. NIST hopes to enlist that semiconductor expertise to build cheap quantum computers using existing microwave technologies. Microwaves have been shown in the past to have an effect on individual trapped ions, but NIST claims to be the first lab to demonstrate quantum entanglement using microwaves.

By positioning microwave ion traps just 30 microns apart, NIST's experimental setup was able to demonstrate entanglement. A laser was still needed to cool the device before use, but a cheap semiconductor version similar to those used in laser pointers was all that was needed. Ordinarily, quantum entanglement requires large, expensive lasers.

"Quantum computers could eventually look like a smart phone combined with a laser pointer-like device," said NIST physicist Dietrich Leibfried. "Sophisticated machines might have an overall footprint comparable to a regular desktop PC."

Gold ion trap on aluminum nitride substrate entangle two ions using microwaves fed into wires from the three thick electrodes at the lower right.

The microwaves in the NIST experiment were used to rotate and entangle the spins of magnesium ions, two operations that will be curtailed to performing logic operations in future quantum computers. The ions were held in place by electromagnetic fields generated by gold electrodes onto an aluminum nitride substrate. Microwave radiation was then applied in the 2-gigahertz band similar to that used by cell phones, resulting in controlled rotation and entanglement of their spins states about 76 percent of the time. The NIST team is now working to improve its success rate to above 99.3 percent, which is the best rate achieved with lasers to date.

Funding for the project was provided by Intelligence Advanced Research Projects Activity, Office of Naval Research, Defense Advanced Research Projects Agency, National Security Agency and Sandia National Laboratories.

It is interesting to watch quantum computing technology emerge - it reminds me of the primitive early transistor prototypes. I expect we'll continue to see multiple efforts to find the working quantum computing paradigm. With success, there will be a sudden leap from single junction devices to the millions that we now take for granted in traditional computing devices.